linux-kernel - [PATCH] drm/komeda: fix 32-bit komeda_crtc_update_clock

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Message-Id: <20190617125121.1414507-1-arnd@arndb.de>
Date:   Mon, 17 Jun 2019 14:51:04 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     "James (Qian) Wang" <james.qian.wang@....com>,
        Liviu Dudau <liviu.dudau@....com>,
        Brian Starkey <brian.starkey@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     Arnd Bergmann <arnd@...db.de>,
        "Lowry Li (Arm Technology China)" <Lowry.Li@....com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH] drm/komeda: fix 32-bit komeda_crtc_update_clock_ratio

clang points out a bug in the clock calculation on 32-bit, that leads
to the clock_ratio always being zero:

drivers/gpu/drm/arm/display/komeda/komeda_crtc.c:31:36: error: shift count >= width of type [-Werror,-Wshift-count-overflow]
        aclk = komeda_calc_aclk(kcrtc_st) << 32;

Move the shift into the division to make it apply on a 64-bit
variable. Also use the more expensive div64_u64() instead of div_u64()
to account for pxlclk being a 64-bit integer.

Fixes: a962091227ed ("drm/komeda: Add engine clock requirement check for the downscaling")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/gpu/drm/arm/display/komeda/komeda_crtc.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c b/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
index cafb4457e187..3f222f464eb2 100644
--- a/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
+++ b/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
@@ -28,10 +28,9 @@ static void komeda_crtc_update_clock_ratio(struct komeda_crtc_state *kcrtc_st)
 	}
 
 	pxlclk = kcrtc_st->base.adjusted_mode.clock * 1000;
-	aclk = komeda_calc_aclk(kcrtc_st) << 32;
+	aclk = komeda_calc_aclk(kcrtc_st);
 
-	do_div(aclk, pxlclk);
-	kcrtc_st->clock_ratio = aclk;
+	kcrtc_st->clock_ratio = div64_u64(aclk << 32, pxlclk);
 }
 
 /**
-- 
2.20.0